1. Field of the Invention
This invention relates to an internal combustion engine and a method for operation of an internal combustion engine. This invention also relates to thermochemical recuperators and the use of thermochemical recuperators as fuel reformers for providing reformed fuel to a reciprocating internal combustion engine.
2. Description of Related Art
Natural gas is the most abundant energy source available after coal. People are looking for more ways to use natural gas as fuel because it is inexpensive and burns very cleanly relative to other energy sources, particularly with respect to coal. In addition, because natural gas is in abundant supply, using more natural gas as an energy source provides a means for reducing dependence on imported foreign oils.
Over the past several years, fuel cells, which typically use hydrogen (H2) as a fuel, have been receiving a substantial amount of attention due to their almost emission-free operation. The primary exhaust from a fuel cell using hydrogen, as with other systems in which hydrogen is used as a fuel, is water. It will, thus, be apparent that substantial environmental benefits may be realized from the use of hydrogen as a fuel in other applications as well, such as internal combustion engines, including reciprocating internal combustion engines and gas turbines. In particular, the hydrogen in the fuel extends the lean operating range of an engine and increases the burning velocity, thereby increasing the combustion rate. Thus, in addition to the environmental benefits, the use of hydrogen as a fuel in internal combustion engines also increases combustion and engine efficiencies, thereby increasing fuel economy. However, one problem associated with the use of hydrogen in such applications is the requirement for ready availability of the hydrogen in a form suitable for use therein. Thus, one issue which needs to be addressed is the production of H2 in a manner which satisfies the availability requirements.
Several reforming technologies to produce H2 are known, including autothermal reforming, partial oxidation reforming, plasma reforming, and steam reforming. Reforming of natural gas or other hydrocarbons produces H2-enriched products which, in addition to H2, may also include CO, CO2, and carbon. At the present time, about 90% of the hydrogen produced around the world is from reforming natural gas, as a result of which demand for natural gas is increasing considerably. Recently, efforts to develop various kinds of fuel reformers to reform liquid or gaseous fuels to produce H2-enriched fuels have increased substantially. Most of these reformers use steam reforming technology, which requires heat and steam.
In a typical reciprocating engine system, a significant amount of energy is wasted. Thus, if this energy can be used to reform a lower quality fuel to higher quality fuel, engine efficiency will increase significantly.
The use of a thermochemical method for fuel reforming employing steam was first suggested in 1964. Since then, the use of a thermochemical method employing combustion products or flue gases from coal and natural gas combustion also has been proposed (See Nosach, V. G., Energy of the Fuel, U.S.S.R., 1989 and Nosach, V. G., “Increasing the Effectiveness of Fuel Utilization in Power Generation, Industry and Transportation”, U.S.S.R., 1989.). However, most of these works were directed to gas turbines and industrial furnaces. The application of thermochemical recuperation to internal combustion (IC) engines was first introduced by O. B., Lindström in 1975. U.S. Pat. No. 3,918,412 to Lindström teaches a method and apparatus for reducing the amount of polluting components in the exhaust gases from internal combustion engines in which a fuel, before being delivered in a gaseous state to the combustion zone or chamber of the engine, is passed through a reforming reactor having a reforming catalyst disposed therein to convert at least a portion of the fuel to carbon monoxide and hydrogen by reaction with steam and carbon dioxide. A portion of the exhaust flow from the internal combustion engine is delivered to the reformer and mixed there with the fuel being delivered to the reformer. The heat content of the exhaust gas is used for the energy requirement of the reforming reaction and the steam and carbon dioxide present as combustion products in the recirculated exhaust gas are used in the reforming reaction. In accordance with one embodiment, air is introduced into the reforming reactor to promote the combustion of fuel and/or reforming reaction products therein. This combustion of fuel and the products of the reforming reaction is adapted such that the reforming reaction is essentially isothermal at a suitable reforming reaction temperature that varies according to the type of reforming catalyst and fuel.
Since the late 1980s, a significant amount of research has been conducted on the use of exhaust gas recirculation (EGR) reforming incorporated into an internal combustion engine. In particular, bench-scale testing has been performed using n-heptane and gasoline. The focus of exhaust gas recirculation reforming was an automotive application using extreme lean-burn conditions. For industrial furnaces, before fuel reforming using the thermochemical recuperation concept was introduced, the primary exhaust energy recuperation was used to preheat the combustion air. This concept has been employed in an engine, termed an “isoengine”, having separate cylinders for compression and combustion, where the combustion air after compression is heated by the exhaust energy in a recuperator.